Esters have long been used as lubricating oils. In fact, esters were the first synthetic crankcase motor oils in automotive applications. Today, they are used in a variety of lubricant applications ranging from jet engines to refrigeration.
Ester-based lubricants, in general, have excellent lubrication properties due to the polarity of the ester molecules of which they are comprised. The polar ester groups of such molecules adhere to positively-charged metal surfaces creating protective films which slow down the wear and tear of the metal surfaces. Such lubricants are less volatile than the traditional lubricants and tend to have much higher flash points and much lower vapor pressures. Ester-based lubricants are excellent solvents and dispersants, and can readily solvate and disperse the degradation by-products of oils, thereby reducing sludge buildup. While ester-based lubricants are relatively stable to thermal and oxidative processes, the ester functionalities give microbes a handle to do their biodegrading more efficiently and more effectively than their mineral oil-based analogues.
Production of such esters (i.e., esters suitable for use as lubricants), however, is generally more involved and considerably more costly than the preparation of their poly-alpha-olefin (PAO) counterparts. As a result, such esters tend to be blended with other base stocks (synthetic and/or non-synthetic) so as to advantageously impart at least some of their lubricant properties, but with more favorable overall economics.
Currently, a variety of commercially-available esters are available for such above-described application. These include mono-esters, diesters, phthalate esters, trimellitate esters, and polyol esters. These are all, however, either generally poor lubricants/lubricant additives (for one or more of a variety of reasons) or relatively expensive.
In view of the foregoing, a more economical lubricant formulation comprising a diester component, particularly wherein said component is at least partially derived from a renewable resource, would be highly desirable.